The present invention relates to an AD converter and a solid-state imaging apparatus using the same. More particularly, the invention relates to an AD converter to convert an analog signal into a digital signal and a solid-state imaging apparatus using the AD converter.
A solid-state imaging apparatus such as a CMOS (Complementary Metal Oxide Semiconductor) sensor includes more than one pixel circuit arranged at more than one row and column. Each pixel circuit corresponding to the selected row outputs an analog signal at a level corresponding to the amount of incident light. The columns are provided with more than one AD (Analog to Digital) converter. Each AD converter converts an analog signal output from the pixel circuit at the corresponding column into a digital signal.
Such a solid-state imaging apparatus includes an increasing number of AD converters as the number of pixels increases. To shorten the processing time, more than one AD converter simultaneously performs AD conversion on output signals from pixel circuits corresponding to the selected row. The AD converters are provided with a bias voltage supply line in common to decrease consumption current or reduce a chip area. The AD converter configuration is simplified.
The solid-state imaging apparatus disclosed in patent document 1 suppresses a power supply noise when more than one comparison circuit operates. For this purpose, the solid-state imaging apparatus uses different bias current values for the comparison circuits and thereby applies different operation timings to the comparison circuits.
The solid-state imaging apparatus disclosed in patent document 2 suppresses an effect of power supply noise on a comparison circuit. For this purpose, a capacitor is coupled between a power supply line and a signal line to feed a potential variation on the power supply line back to the signal line.    Patent Document 1: Japanese Unexamined Patent Publication No. 2009-118035    Patent Document 2: Japanese Unexamined Patent Publication No. 2007-281540